The CD43 molecule, also called sialophorin or leukosialin, is a cell-surface molecules expressed on most of hematopoietic cells except erythrocytes. Human CD43 has a mucin-like extracellular domain of 235 amino acids (aa), a transmembrane domain of 23 as and a 123 as intracytoplasmic domain, all encoded by one exon (Pallant et al., Proc Nall Acad Sci USA. 1989, 86:1328-32; Shelley et al., Proc Natl Acad Sci USA 1989, 86:2819-23). The extracellular domain of human CD43 is rich the amino acids serine (46 residues) and threonine (47 residues), most of which carries about 80 0-linked carbohydrate chains. In addition, CD43 carries 1 N-linked carbohydrate chain. The structure of these O-glycans varies from one cell type to another (Carlsson et al., J Biol. Chem. 1986, 261:12787-95).
The CD43 gene consists of two exons, separated by a 378 by intron, whereby the entire translation product is encode by the second exon (Shelley et al., Biochem J. 1990, 270:569-76). CD43 has been believed to be a specific leukocyte-type marker restricted to most of leukocytes, platelets and hematopoietic stem cells, except for erythrocytes (Remold-O'Donnell et al., Blood 1987, 70:104-9; Fukuda, Glycobiology. 1991, 1:347-56). However, the expression of CD43 in human tumor cells of non-hematopoietic origin, such as a human uterine cervix cancer cell line (CaSKI), a human lung cancer cell line (A549), a human breast adenocarcinoma cell line (MCF7), a human fibrosarcoma cell line (HT 1080), and human colonic adenocarcinoma cell lines (COLO 205, HT 29, Caco-2, DLD-1 and SW480), has been demonstrated (Fernandez-Rodriguez et al., Tumour Biol. 2002, 23:193-201). CD43 is also expressed in human colon cancer tissue (Sikut et al, Int J Cancer. 1999, 82:52-8; Jung et al, Korean J Pathol. 38:8-14).
Biosynthetic studies show that the CD43 precursor, with a predicted size of around 40 kDa (including one N-glycan), migrates with an apparent molecular mass of 54 kDa upon electrophoresis. This precursor is subsequently converted to a mature glycosylated molecule with sized from 115 kDa to up to more than 200 kDa due to variable glycosylation. Thymocytes, CD4+ T lymphocytes and monocytes express more of a 115 kDa isoform, whereas a 130 kDa form is found mostly on activated CD4+ T cells, CD8′ resting and activated T cells, neutrophils, platelets and B cells (Rosenstein et al., Immunol Res. 1999, 20:89-99). It seems that more than one isoform can be co-expressed on the surface of the same cc 11. A tightly regulated post-translational 0 glycosylation pattern results in these characteristic molecular weight isoforms that are differentially expressed in different cell types. Especially, expression of core 2 p-1,6-N-acetylglucosaminyltransferase (C2GnT) results in expression of the 130 kDa CD43 isoform in thymocytes and T cells (Piller et al., J Biol. Chem. 1988, 263:15146-50).
Until recently, more than 17 anti-human CD43 antibodies had been reported. Most of these antibodies react with carbohydrate epitopes on the extracellular domain and all known anti-CD43 antibodies detect the CD43 protein expressed on mature hematopoietic cells (Table 1). Thus, they are not efficient at detecting or eradicating leukemic or lymphoma cells.
TABLE 1Anti-CD4antibodyCD43-positive cellsCD43-negative cellsEpitope*ReferenceT305Activated CD4+ cells,Granulocytes,Core-21, 2CD8+ T cells,erythrocytes, plateletsthymocytes, myeloidcarbohydrateprecursors in bonemarrowL10T cells, thymocytes, BErythrocytes1-78 Sialidase-3cell lines, monocytes,resistantneutrophils, platelets178L2T cells, thymocytes, BErythrocytescell lines, monocytes,neutrophils, platelets84-3C1Bone marrow cells,Platelets,Sialidase-sensitive4thymocytes, T cells,erythrocytescarbohydratemonocytes,granulocytesMEM-59Most of leukocytes,Neuraminidase-5, 6CD34+ bone marrowsensitivecellscarbohydrateMT-1, L60T cells, monocytesB cellsNeuraminidase-7DFT1T cells, monocytesB cellssensitivecarbohydrate1G10T cells, NK cells,B cells, Erythrocytes8granulocytesCBF.78T cells, subsets ofNeuraminidase-9monocytes andresistantgranulocytesRDF/AD-9T cells, monocytes,B cellsNeuraminidase-granulocytessensitivecarbohydrate161-46T cells, monocytes,B cellsNeuraminidase-granulocytesresistant4D2COLO 205, K562,Intracellular (337-34310 Jurkat4D1Activated CD4+ T cells,B cellsCore-2Mukasa et al.,monocytescarbohydrate1999*1. Fox et al., J Immunol. 1983, 131: 762-7; 2. Saitoh et al., Blood. 1991, 77: 1491-9; 3. Remold-O'Donnell et al., Blood. 1987, 70: 104-9; 4. Borche et al., Eur Jlmmunol. 1987, 17: 1523-6; 5. Stefanova et al., Folia Biol (Praha). 1988, 34: 255-65; 6. Alvarado et al., Eur J Immunol. 1995, 25: 1051-5; 7. Stross et al, J Clin Pathol. 1989, 42: 953-61; 8. Horejsi et al., 1997, In Kishimoto T, et al, Leucocyte Typing, Vol. VI: White Cell Differentiation Antigens 494. Garland, New York and London; 9. Tkaczuk et al., Tissue Antigens. 1999, 54: 1-15; 10. Sikut et al., Int J Cancer. 1999, 82: 52-8; 11. Mukasa et al, Int Immunol. 1999, 11: 259-68.